Molecular pumps are attached as vacuum pumps for creating an ultra-high vacuum to various processing apparatuses represented by, for example, semiconductor manufacturing apparatuses, various analytical apparatuses, electron microscopes, and the like. A molecular pump generally includes a pump body provided with a turbo molecular pump portion including rotor blades and stator blades, and a control unit that accommodates a control portion for controlling the operation of the turbo molecular pump portion and a power supply portion for supplying electric power for driving the turbo molecular pump portion.
In the molecular pump, the power supply portion included in the control unit includes a booster circuit, a converter circuit, an inverter circuit, and the like, which are sources of heat generation, and it is thus necessary to appropriately cool these components. Similarly in the pump body, heat is generated at motors for causing rotation of a rotor having rotor blades, a bearing that supports a rotation shaft for causing rotation of the rotor, and the like, and it is thus necessary to appropriately cool these components.
Hence, a molecular pump is known to which a liquid cooling-type cooling unit through which a cooling liquid can be circulated is attached. Japanese Patent Laying-Open No. 11-173293 (PTD 1), for example, discloses a molecular pump wherein a cooling unit is sandwiched between a pump body and a control unit, and Japanese Patent Laying-Open No. 2011-27031 (PTD 2) discloses a molecular pump wherein a pump body and a control unit are arranged side-by-side on a cooling unit.
Generally, the control unit is often of a semi-hermetic-type communicating with the outside and having a drip-proof structure and a dust-proof structure whereby entry of liquid drips and dust particles is appropriately prevented. In this case, the dew-point temperature inside the control unit is equal to the dew-point temperature of an ambient environment. Therefore, the portion where the above-described cooling unit is arranged in contact therewith or close thereto has a locally low temperature, and if this temperature decreases below the dew-point temperature, condensation will form on this portion.
If such condensation forms, attachment of a condensation liquid to the above-described various circuits may cause a failure or a malfunction. It is thus necessary to inhibit the formation of condensation inside the control unit as much as possible.
To inhibit the formation of condensation, Japanese Patent Laying-Open No. 2009-174333 (PTD 3), for example, discloses a molecular pump wherein a pipe through which a cooling liquid can be circulated inside a control unit is installed, and a condensation sensor is mounted inside the control unit, so that the circulation of the cooling liquid is stopped when condensation is detected by the condensation sensor.